'Game breeds' are chickens who were, or are, bred for cock fighting, which is still legal in parts of the USA, and many other countries. These birds are really the 'original' domestic chickens, and can look more like the wild jungle fowl than most other modern breed types.
Think 'upright' and muscular, and tight feathering. Cockerels, and cock birds, of many of these breeds, will kill each other, and need to be housed separately. Great mothers, and human friendly. I've never had any, because I want roosters who will be compatible with each other instead.
I think it's the Malay roosters who can be up to three feet tall!
Mary